extraordinary. reporter: 600 feet down and 3 miles along a dark narrow tunnel. the culmination of a 7-year, $817 million project. this is the end of the tunnel and this is the critical points. you above us 40 feet is the catch. think of it has a giant bathtub. above that waters of lake mead. and in a few of weeks time that plug will be lifted and the waters will flood the tunnel. it will guarantee the water supply for this i las vegas. even as it leaves the other two turns above water line useless. it s the economic engine to the state of nevada. this is a responsibility we